1. Field of the Invention
The invention relates to agricultural carts used for transporting plant materials, such as nursery stock or potted plants, typically in a greenhouse environment and environs. More particularly, the invention relates to improved removable shelves for the aforementioned carts that do not create excessive noise due to shelf vibration when the cart is being moved.
2. Description of the Prior Art
In the greenhouse industry, carts are used to transport plant materials, such as nursery stock or potted plants. The carts have front and rear sets of wheels mounted to the underside of a base frame with a vertical pillar extending upwardly from each corner of the frame. At least one horizontal shelf is provided for supporting the plant materials being transported. The shelf may be attached to each vertical pillar, for example, by means of a hook at each corner of the shelf that is adapted for engagement in a corresponding slot at a pre-determined height on the vertical pillar. This allows the shelf to be readily removed from the cart or positioned at a different desired height.
The shelf is typically formed from L-shaped frame members of a galvanized metal material that are typically attached to one another, for example by welding, to form a substantially rectangular frame. The L-shaped members are oriented such that the frame has a horizontal flat surface inward of an upwardly extending rim. A planar shelf element is placed within the rim and supported by the flat surface of the frame. A plurality of frame cross-members may be provided across the width of the shelf at discrete intervals along the length of the frame to provide additional support to the shelf element. The shelf element is typically made from a galvanized sheet material or may alternatively be made from plywood or a perforated material, such as expanded metal, to allow dirt and debris to fall through the shelf element.
The shelf element is typically attached to the horizontal surface of the frame by means of fasteners, such as, for example, rivets. The rivets protrude from the bottom of the frame and can potentially cause injury to persons removing the shelf. When galvanized metallic materials are used to construct the shelf element, the riveting process requires the material to be punctured, thereby exposing an un-galvanized surface to environmental conditions with the potential for rust formation. As an alternative to riveting, a metallic shelf element is sometimes attached to the frame by means of spot welding. The spot welding process is well known to cause a loss of the galvanized coating from metal parts, again creating the potential for unsightly rust formation. Spot welding also creates a region of localized heating that embrittles the shelf element, leading to premature mechanical failure. Plywood shelf elements are typically attached to the frame by riveting as previously described. Over time, differences in the rate of thermal expansion of the frame and shelf element cause the holes formed by the rivets in the shelf element to oblate. This tendency towards oblation is exacerbated by vibration of the shelf element when the cart is in motion and eventually results in loss of attachment.
Since the bottom surface of the shelf element is in direct contact with the horizontal planar surface of the frame, vibration of the shelf element due to motion of the cart causes the shelf to rattle. The rattling produces a significant amount of noise, regardless of the material of construction of the shelf. The noise level created when transporting a plurality of concurrently rattling shelves poses a health and safety issue for greenhouse workers; accordingly, abatement of shelf noise levels is a top priority for greenhouse management.
The present invention seeks to address the aforementioned maintenance problems and moreover to reduce undesirable health and safety issues such as excessive greenhouse noise levels by providing an improved shelf for an agricultural cart.
According to the present invention, there is provided a cart for transporting plant material having a rectangular-like base frame with wheels thereunder and at least one shelf. The cart comprises vertical pillar members extending upwardly from the base frame for supporting the shelf therebetween, each pillar having first attachment means. The shelf has a frame, the frame having a planar surface for supporting a shelf element thereon. The shelf element is attached to the planar surface by an adhesive material having a resiliently deformable thickness. The shelf element is vertically separated from the planar surface by the thickness of the adhesive material to thereby reduce the vibration of the shelf element. The frame has second attachment means complementary to the first attachment means for removable attachment of the shelf to each pillar.
According to another aspect of the present invention, there is provided a method of assembling a shelf for a cart used to transport plant materials. The method comprises the following steps: preparing a rectangular-like frame having planar surfaces for supporting a shelf element thereon; applying a resiliently deformable adhesive material to the planar surfaces; positioning a shelf element above the planar surfaces; applying the shelf element into engagement against the adhesive material; curing the adhesive material under ambient conditions.
Further features of the invention will be described or will become apparent in the course of the following detailed description.